EGADS2SRF Version 7.6

The input geometry file should have a name like [geom].stp, [geom].igs, [geom].iges, or [geom].egads, where [geom] is the name of the geometry. Input and output file names assumed by egads2srf are based on a rootname, constructed by appending 3 digits to the geometry file base name [geom], e.g., rootname = [geom].001, [geom].002,... where the 3 digits corresponds to the solid id number in the geometry file. For a geometry file with one solid, the rootname would be geom.001.

Geometry defects described in EPOGS_Workflow.pdf could potentially affect the success on running EPOGS to completion or the quality of the resulting grids. If such defects are present, it is best to remove them prior to using EPOGS.

Users are highly encouraged to work through the EPOGS tutorial under chimera3.0/tutorials/epogs.

• Input geometry file in STEP, IGS or EGADS format with file name extension .stp, .igs, or .egads where the file should contain at least one BREP solid
• A geometric components data file with filename rootname.gcomp that contains the list of BREP faces belonging to each geometric component

• rootname.face - ASCII text file containing max grid spacing and max dihedral angle for each BREP face

   A sample gcomp data file with 3 components and 45 BREP faces is shown below:
   --------
   Fuselage
   12:20,32:41

   LeftWing
   21:31,42,44

   RightWing
   1:11,43,45
   ---------

• rootname.i.tri - an unstructured surface triangulation (one entity in CART3D .i.tri format)
• rootname.triq - an unstructured surface triangulation with u,v parameter values at vertices of each BREP face (NFACE entities in CART3D .triq format)
• rootname.uvin - a set of structured surface patches from forward evaluation of auto-determined parameter space locations on each face driven by max dihedral angle, max cell size, and max chordal deviation inputs. Vertices in trimmed regions are tagged by the iblank value (NFACE surface grids in PLOT3D format)
  • iblank = 1 (vertex is on geometry)
  • iblank = 0 (vertex is outside geometry)
• rootname.uv - PLOT3D function file containing u,v values at vertices for each face in rootname.uvin
  • fun 1 = u
  • fun 2 = v
• rootname.cur - discretized BREP edges on geometry (NEDGE surface curves in PLOT3D format)
• rootname.cuv - PLOT3D function file containing edge vertex u,v values for each edge in rootname.cur
  • fun 1,2 = u,v on face 1 associated with edge
  • fun 3,4 = u,v on face 2 associated with edge; u=v=0 if face 2 is empty as on open boundary
• rootname.topo - ASCII text file containing topological information for edges and faces
• rootname.pogs.i - ASCII text file containing input parameters for running pogs
• rootname.face - ASCII text file containing max grid spacing and max dihedral angle for each BREP face (scaled by component size)
• rootname.frm.gcomp - geometric components data file with reduced face list if faces are removed for open geometry cases

• rootname.half.gcomp - geometric components file analogous to rootname.gcomp but for + side faces and components only
• rootname.half.i.tri, rootname.half.uvin, rootname.half.uv, rootname.half.cur, rootname.half.cuv, rootname.half.topo - half-body versions of the corresponding full-body files

• egads2srf.log - a log of the command line arguments from the most curent run

  egads2srf [-i ifile] [-b bodygen] [-isym sym] [-frm frmstring] 
            [-maxa maxang] [-maxc maxchord] [-maxe maxedge] [-maxsr srmax] [-npmin np]
            [-dswall dsw] [-stenqual sq] [-stop stoploc]
            [-smedge smalledge]  [-epst epstd] [-u units] [-scale scfac] [-c] [-r] [-help]

All arguments are optional except for ifile. If an argument is omitted, the defaults in the following table are used. A log file called "egads2srf.log" is automatically generated that contains the most recent command line arguments.

Argument	Description	Default
ifile	input file containing geometry (igs or step)	(not read)
bodygen	Create tessellations for solid body number = bodygen only (for cases with multiple solid bodies)	tessellate all bodies
sym	Symmetry specification 0 : no symmetry specified 1/2/3 : geometry is a half body on the +x/+y/+z side; -1/-2/-3 : geometry is a half body on the -x/-y/-z side; 11/12/13 : geometry is a full body symmetric about x=0/y=0/z=0	0
frmstring	List of faces to remove from meshing domain (open geometry)	e.g., 3,8,15:17
maxang	Max allowed dihedral angle in degrees	5.0
maxchord	Max allowed chordal deviation > 0 take value as input < 0 take absolute value times global bounding box diagonal arc length as input	-0.001
maxedge	Max allowed arc length of triangle edge or structured mesh spacing > 0 take value as input < 0 take absolute value times global bounding box diagonal arc length as input	-0.025
np	Minimum number of points in each direction in u, v tessellation	9
dsw	Wall normal spacing for volume grids	1.0e-4
sq	Fringe points with donor stencil stenqual quality below sq will be tagged as an orphan points (0.0 < sq <= 1.0)	1.0
stoploc	Stopping location. Allowed options are: contents - Run in inquiry mode to report contents only (number of solids, faces, edges, nodes) faces - stop after writing guvo.sur to be used in construction of gcomp file	none specified
units	Convert output grid files to different unit assuming input geometry has been interpreted in mm. Use this option only if egads2srf could not determine units from input geometry file (in/ft/m/cm)	no conversion
scfac	Scale all output grids (i.tri, .cur, .uvini) by scale factor scfac	1.0
smalledge	Remove edges smaller than smalledge	0.0
epst	Extend uv bounding box of triangles by epst * triangle bounding box diagonal (increase this parameter slightly to unblank more points on uv structured patches)	0.01
-c	Run in inquiry mode to report contents only (number of solids, faces, edges, nodes)
-r	Re-run using parameters stored in egads2srf.log

1. Given an input geometry file with filename = geom.stp, geom.igs, or geom.egads, examine the contents of this file by

   egads2srf -i filename -stop contents >! e.o

   Check that the file contains at least one solid. If more than one solid exists, generate the files for each solid in a separate directory using the "-b" option.

2. Run egads2srf to write the faces to a file called guvo.sur (plot3d format)

   egads2srf -i filename -stop faces >! e.o

   Load guvo.sur into OVERGRID (or an equivalent visualizer) and construct the geometric components data file (.gcomp) in a text editor.

3. Run egads2srf with the target global grid control parameters

    egads2srf -i filename [-isym sym] [-frm frmstring] 
            [-maxa maxang] [-maxc maxchord] [-maxe maxedge] [-maxsr srmax] [-npmin np]
            [-dswall dsw] [-stenqual sq] >! e.o 
   

   Examine the output .uvin and .i.tri files to determine if the mesh resolution is adequate. Adjust the global control parameters and rerun if needed.

4. Look for potential geometry defects by examining the various outputs (see EPOGS_Workflow.pdf for more details). These may include
   • extremely small edges (see histogram of edge arc lengths in standard output e.o)
   • spurious nodes (see .uvin and .cur files in OVERGRID)
   • extremely small faces (see .uvin file in OVERGRID)

5. Local component maximum grid spacings are automatically scaled relative to the global maximum grid spacings by a scale factor determined by the ratio of the component bounding box diagonal to the global bounding box diagonal. If more specific grid spacing control is needed, adjust the appropriate parameters in the auto-generated rootname.face file and rerun.